•
"
.,;
C.M. 1995/M:28
.ANACAT Fish Cömmittee
ICES C.M. 1995
., .
.
~
WILD BAlTIC. SALMON STOCKS: FECUNDITY AND BIOLOGICAl
.
REFERENCE POINTS CONCERNING THEIR STATUS
"
~
Also Romakkaniemi 1).
Lars Kar1sso'n 2) & Östen Karlström 3)
1) Finnish Game & Fisheries Research institute
Bothnian Bay Fisheries Research Station
Simontie 9
. 95200 Simo
FINLAND
•
2) Swedish Salmon Research Institute
. Forskarstigen
S-814 94 Älvkarleby
SWEDEN
3)Swedish National Board of Fisheries
Research Office Lulea
Skeppsbrogatan 9
S-972 38 Luleä
SWEDEN
ABSTRACT
The use cif biological reference points in the assessment of the Saltic salmon was
examined and evaluated. lricreased knowledge of the productivity of Baltic rivers
combined with data obtairied from monitoring escapement arid the resulting smolt
production were found to be critical in improving the precisicin and applicability of
the biolcigical reference points. In initial trials aimed at calculating an e9g deposition
requirement for a potential production level in the Gulf of Bothnia rivers, a range of
70 - 700 eggs/100 2 of salmon nursery area was obtained. The egg deposition.
requirement for the Gulf of Bothnia stocks seems to be considerably lower than that
for most North Atlantic salmon stocks. Studies on the productivity of the Baltic
.
salinon rivers and specific stock-recruitment investigations are needed in order to
establish more precise referEmce points and egg deposition targets in the Baltic
region. However, studies from outside the. Baltic area combined with Baltic studies
on productivity levels in the salmon populations may be used to give ranges of
suitable egg deposition levels and also provisionai targets.
m
The reproductive potential of BalÜc salmon was assessed by examining fecundity
data from the wild salmon stocks iri the Gulf of Bothnia. A fecundityof 1 200-1 500
eggs/kg .cf female salmon was found to prevail among the wild salmon stocks in the
Gulf of Sothnia. Relative reproductive values for Saltic salmon of different ages were
calculated based on the sex ratio and mean weigtit for eacti age-class. The relative
reproduciive value of salmon was found to rise steeply witti sea age.
2
1. introduction
leES
The international Saltic Sea Fishery Comission has asked the,
for scientific
adviceto help attain the management goal of "safeguarding of wild salmon stocks".
What this objective means in terms of biological refererice points is a questiori of
debate. The status of Baltic salmon stocks has generally been poor for several
.
decades, and there is lack of weil documented examples of what a t'good status of
stocks" would mean in Baltic. Thus it is important to examine possible
interpretations of management targets for Baltic salmon. Another good reason for
such an evaluation is that the improved monitoring techniques recently developed
might allow ci new assessment system, based on weil defined reference points, to be
set up.
e-
ane recent einphasis in tne management of North Atlantic salmori stocks has been
to establish egg deposition and spawning stock targets, which are based on the
studies of biological reference points in the stock-recruitment relaÜonship. This
management regime aims at conserving resources by maximising/optimising
recruitment while minimizing the risk of stock collapse arid 1055 of genetic diversity.
The approach requires studies on the productivity of the river systems and the
fecundity of salmon stocks and a means of monitodng the size of the spawning
'
stock and the corresporiding smolt output.
The followlng seetions describe the recent status of Baltic salmon assessment work
concerning biological reference points. Possibilities to develop assessment towards
egg deposition/spawning stock targets were studied in some example Hvers. Special
emphasis has been placed on fecundity data because efforts thus far to exainine the
fecundity of Baltic salmon have been limited.
2. Currerit biological reference points in the Saltie
2.1 Reference points and their interPrE!tatiori
Baltie reference points used thus far have included
- the potential smolt production in the rivers supporting wild stocks
- the potential density level of parr in the rivers
- river catch
Current values !lava been compared with corresponding potential or histoHeal
values without ariy analysis. Using river catch as an index of stock status is a
preposterous approach, even though river catch and spawning stock siie must be
related to some extent. Usually these reference points have beeri used only as ,
exainples of what a good status of the wild stocks could mean. Lass commonly, they
have beeri considered as real target values.
,
There are two advantages of the above-mentioned approach:
,
- some relatively comparable historical data concerning the monitored
variables are ;,ow available
,- updating of the variables does not require too much work
.
3
The corresponding disadvantages are as folIows:
.,
- the approach does not take into account the dynamics of the stockrecruitrnent relationship or the variability in prciduction capacity iri nature
- it is difficult to convert tne reference points to escapement values arid
.
to link tnem to real management proposals .
- M74 has weakened tns relationship betWeeri the parent stock arid the
production cif parr and srnolt; it is therefore difficult to evaluate
.
management success in terms of escapement, which is a direct object of
fisheries management
No long-term studies of the stock-recruitment relationship have beeri carried out in
tne Baltic region. As stated earlier, estimates of parr denstity levels and smolt output
have been made, but IiUle is known about the adult stock, not to mention the stockrecruitment relationship.
'
2.2 Estimation
of the refere,nce points
Vah..ies have often been established for the purpose of compensatory readng or
stock enhancement readng. Potential smolt and parr prciduction levels have been
designated on tne basis of data obtained using several approaches: analysis of
historical records, habitat inventories, stocklng experiments, etc. The data in
question are far from precise, and seme inconsistencies can be found between the
values estimated in different ways.
•
Estimates from thres rivers in ths Gulfof Bothnia are given as exarnples, in Table 1 ~
The table also contains a Iittle extra inforrnation about the rivers and their salmen
stocks in order to provide a beUer description of the characteristics of the Baltic
salmon and it's freshwater habitat.
The production capacity of salmon in Baltic rivers is, on average, lower than that of
salmon in most other European and Canadian salrnon rivers. For example, the .
potential smolt production in the rivers emptying into the Gulf of Bothnia is estimated
to be 1-3.5 smolts/100 m2 of nursery area (Karlström 1977, Jutila & Pruuki 1988,
Kemppainen et al. 1995), which corresponds to approx. 0.3-1.5 smolts/100 m2 of
f1uvial habitat accessible to salmon. By contrast, a smolt production potential of 3
smolts/100 m2 of fluvial habitat is considered to be the average level in Atlantic
Canadian rivers, and this level has been considered as too low for Atlantic
European rivers (Anon. 1994). Productivity in the southern Baltic rivers is assumed
to be c10ser to the level observed elsewhere in Europe (Karlströrn 1977).
3. The fecundity of Baltic sahnon
3.1 Material and methods
Data on fecundity for a number of wild salmon stocks in the Gulf of Bothnia were
obtained from the sources giveri in Table 2. The mean fecundity of a number of
females was calculated using the equation
e
•
4
Mean fecundity= Sum of eggs/Sum of fish weights
Most of the salmon females were of wild origin. The data ware collected when
stdpping salmon females in the autumn. Ttle number of eggs per litre of rae was
normally estimated usirig the so ealled Brofeld seale, which is based on the number
of egg5 needed to cover a length of 25 cm. Data collected in connection with
stripping suggest that it was not always complete; thus fecundity was prabably
underestimated to some extent.
Data used for ealculating sex ratios and mean weights for the different sexes and
age classes were collected from the trap at Norrfors, in the River Urne, where fish
ascending to the River Vindelälven are eaught. Data based an reared salmon
tagged in Sweden over the years 1966- 94 were also used for calcuiating sex ratios.
Tagged salmon originated from the Rivers Lule, Angermanälven and Indalsälven.
3.2 Fecundity and tlla relative reproductive values
Fecundity values from 1 050 to 1500 eggs/kg of female have been reported for
several Baltic salmon stocks (Carlin & Johansson 1971, Brännäs et al. 1985) and.
fecundityis often ässumed to be in a range of 1 100 -1 200 egg/kg (Christensen &
Larsson 1979). Estimates based on the new data presented here, which are mainly
for wild females, are slightly higher (1 200 -1 500 eggsl kg female), not considering
the Rivers Lögde, Byske and Öre, where the stripping is thought to have been the
least complete (Table 2). -rabies 3 and 4 summarize the data collected on ag'e and
sex raUos, as weil as mean weights at different ages, in the Gulf of Bothnia. At ages
of 1SW, 2SW arid 3SW, respectively, females coristitute .about 10 %, 45 % and 80
% of the individuals arid weigh about 2.3 kg, 5.4 kg arid 8.7 kg. The limited amount
of data available on 4SW salmon suggest that the proportion of females is slightly
higner than that of males.·
e
-'''.
Using values for age class specific mean weights obtained from the trap at Norrtors
in 1994 combined with the average values ofsex ratiosmentioned above, we can
calculate the relative importance of salmon af different ages in terms of spawner
fecundity as folIows:
1SW
Relative "alue
1
2SW
10.5
3SW
29.8
The reproductive value of a three-year-old salmon would thus be almost 30 times
that of a 1SW salmon and about 3 times that of a 2SW salmon. However, this
method of calculation does not consider the genetic aspects of stock maintainance
since the genetic variability in a given stock is partly determiried by the actual
number of spawners that it contains.
f.
5
4. Conversion of the potential smolt production values to egg deposition
values - examples trom the Gulf ot Bothnia
Setting up egg deposition targets and the corresponding spawning stock targets on
. the basis of stock-recruitment studies has been judged the most apprcipriate way to
. manage salmon stocks in the North Atlantic (Arien. 1994). A similar approach in the
Baltic region would offer several advantages in terms of standardisation of the ,
methodology. data transportability and comparison. establishment of stock-specific
monitoring etc.
We have chosen ci range of estimate values (up-and-down method), which we find
as most likely when we examine the egg deposition values at a potential production
level for the salmon stocks in the Gulf of Bothnia. These values give the broad
margins for the most sensible egg deposition rates:
Assuming that the potential smolt production level in the salmon nursery
habitat varies between 1 and 3.5 smolts/100 m2 in the Gulf of B o t h n i a "
rivers and assuming that the egg to smolt survival rate varies between
•
0.5 and1.5 %. the egg deposition value would lie somewhere between
70 and 700 egg5/100 m2 of salmon nursery habitat. Conversion of this
range to kilcis,of spawning females and eomparison to highest histcirical
catch levels (Table 1) indicate that we are at a proper level in our
estimates: the lowest and the highest egg deposition values correspond
to a river-fishing exploitation rate of 0.7-0.9 and 0.2-0.4, respectively. in
the Simojoki and Tornionjoki rivers:
In general. egg deposition targets established or suggested elsewhere for Atlantic
salmonare higher than the Gulf cf Bothnia estimate. ranging from approx. 100
eggs/100 m2 of fluvial habitat up to 2 000 - 3 000 egg5/100 m2 of nursery area
(Anon. 1994). This is in accordance with the recorded difference in the potential
smolt prodLiction estimates (see chapter 2.2).The low salmon production capacity in
the Gulf of Bothnia rivers can be explained as folIows:
1) these rivers are located at high latitudes, where productivity is
"'generally lower than further south;
, .
2) they have a relatively diverse fish species composition, suggesting
that habitat availability is limited and that young salmon are subjected to
strong competition for food and a high risk of predatiori;
3) winter coriditions in the area are severe. with a thick ice cover arid
low discharge values that tend to reduce overall productivity.
Although stock-recruitment studies with Atlantic salmon iridicate thai several kinds
cf stock-recruit curves can exist, their shape usually resembles that of an
,
asymptotic curve (ArlOn.1994). Consequently. if maximizing the potential production
level were to be chosen as a management target. overestimating the egg deposition
requirement would be less serious of an error than underestimating it.
Egg deposition values with the range of the most sensible values have been
converted to total egg deposition values and numbers of spawning females for three
rivers: the Simojoki, Tornionjoki andVindelälven (Table 5). A Canadian egg
deposition target have also been calculated for the total f1uvial habitat accessible for
. ..
6
saimon in order to display the meanlng of habitat component in the calculations. The
range of values is naturally very large, because of the wide range, in the eg9
deposition values. The sex ratio in Uie river,is largely determinedbythe sea tisnery
(fishing mortality is higher for females Ulan tor males) which is why egg deposition
values have not been ccinverted to total spawning stock sizes.
.
5.
•
Egg deposition values arid M74
A syndrome called M74 has recently increased mortality among salmon alevins in
the Baltic (Kaflsson and Karlström 1994). The incidence ,af M74, first detected in .
1974, has varied from year to year, and for many years it did not give rise to ariy
major problems. However, in 1992 the frequency of M74 increased dramatically, and
for the pefiod 1992-95 the total mortality caused by M74 in natcheries has been in .
the range Of 40-98% among alevins derived from sea-run females. On the basis of
elecrofishing surveys arid catch statistics the extra mortality caused by M74 in years
1992-94 was estirriated at 75% in rivers having wild salmon stocks in the Gulf of
Bothnia (Karlström1995). Secause the outbreak of M74 was of an unprecendentedly
large magnitude It
weaken the stock-recruit reiationship. In theory egg
deposition values can be adjusted using a factor calcuiated based on the M74
mortality. At present we are of.the opinion that any egg deposition target should be
able to the butter extra mortality caused, for example, by a low to moderate
incidence cf M74. An additional mortality of about 75% over several years should,
however, not be accounted for in anormal egg deposition target. This kind of
mortality must, instead, be treated separately and dealt with using special
management.
will
6. Coricluding remarks and recommeridaticiris for the future activities
It was suggested that the operaticinal interpretation cf the definition of conservation
of Ätlantic salrnon in Canada shciuld be based on the potential productivity of rivers
(CAFSAC 1991). This kind of interpretation supports the use of variables linked to
the fresh water productiori (smolt production, parr densities, egg deposition,
spawning stock). The refererice points linked to escapement and e9g deposition
values seerriespecially usefull from the assessment point of "iew, and we highly
recommend that additional research in this area be carried out in the Saltic.
Research on egg deposition targets, can be divided into two parts, one dealing ,With
potential freswater productivity and the ether with monitodng and developing stockrecruitment relationship. We recommend that the following steps be taken on ttie
research front.
1) The potential production capacity as weil as the factors affecting to the
productivity should be studied further to provide more exact information about the
productivity of ttie Saltic salmen rivers
2) Studies on actual spawning stock size andegg deposition rates and the resulting
smolt production should be started. Such studies would further our understariding of
the dynamics of stock-recruitrnent relatlonships. They would also help us to
J.
••
7
distinguish the influence of M74 freim other mortality factors. Furthermore, with the
actual escapement values that would be obtained, population models ceivering the
sea phase of the life cyCle could be ·developed. There are two goeid reasons for
statiing this kind cf study in orie of the smaller rivers in the Gulf of Bothnia': This
region of the Baltic has the largest potential smolt production, and salmon rivers in
this area are among those most endangered in the Baltie region.
It will certainly take a long time (decades) before any real stock-recruitment
relationship will be established in the Baltic. We recommend that in the meantime
provisional escapement and egg deposition targets based on present knowledge be
established and used as a basis for assessment and management. Such targets
should gradually become more precise and accurate as results from the studies
discussed above start to accumulate.
References
Anon., 1992. Report of the Workshop on Salmon Spayming Stock Targets in the
North-East Atlantic, Bushmills, N. Ireland, 7-9 December 1993. ICES
C.M.1994/M:7. 31 p. + tables & figures.
•
Brännäs, E., Brännäs, K. and Eriksson, L.-O. 1985. Egg characteristics and
hatcherY survival in a Baltic salmon, Salmo salar L., population. Rep. Inst.
Freshw. Res. Drottningholm. 62:5-11.
CAFSAC 1991. Definition of conservation for Atlantic salmon. Canadian Atlantic
Fisheries Scientific AdvisoryCommittee Document 91/15. In: CAFSAC'
Annual Report. Vol. 14. 1991. Department of Fisheries and Oceans. p. 147150.
Carlin, B. and Johansson, N. 1971. Undersökningar över rommängden hos lax i
Ljusnan 1950 och 1970 - en jämförelse. (Comparative studies ein the the
fecundity of salmon in the River Ljusnan in the years 1950 and 1970).
Laxforskningsinstitutet Medd. 8:1-6.
Christensen, O. and Larsson, P.O. 1979. Review of Baltic salmon research. ICES.
Coop. Res. Rep. No 89, 124 p.
Jutila, E. 1987. Lohenpoikastuotannon ja kalansaaliiden kehitys Simojoessa koskien
kunnostuksen jälkeen vuosina 1982-1985. (The development of salmon parr
production and fish catches in the River Simojoki after restoration of the
rapids in the years 1982-1985). Helsinki RKTL. Monistettuja julkaisuja 71. p.
47-96.
Jutila, E. 1992. Report on the management, ,catches and smolt production of the
salmon stock in the Simojoki River. ICES C. M. 1992/M: 11. 14 p.
•
------- - - - -
•
•
L
8
Jutila, E. & Pruuki, V. 1988. The enhancement of the salmon stocks in the Simojoki
and Tornionjoki Rivers by stocking parr in the rapids. Aqua Fennica 18,1. p.
93-99.
Karisson, L. and Karlström, Ö. 1994. The Baltic salmon (Salmo salar L.): its history,
present situation and future. Daria, 10:61-85.
Karlström, Ö. 1977. Biotopval och besättningstäthet hos lax- och öringungar i
svenska vattendrag. (Habitat selection and population densities of salmon
and traut parr in Swedish rivers). Inf. from Sötvattenslaboratoriet
Drottningholm 6. 72 p.
Karlström, Ö. 1995. Salmon parr (Salmo salar L.) praduction and spawning stocks in
Baltic salmon rivers in northern.Sweden 1976-1994. ICES C.M. 1995/M:33.
Kemppainen, S., Niemitalo, V., Lehtinen, E. ja Pasanen, P. 1995. Lohen ja
meritaimenen istutustutkimukset Kiiminkijoella. (Stocking researches with
salmon and sea trout in the River Kiiminkijoki). Helsinki RKTL.
Kalatutkimuksia - Fiskundersökningar. (Manuscript)
Romakkaniemi, A 1988. Tornionjoen vesistön lohen ja meritaimenen
poikastuotantoalueiden inventointi. (The habitat inventory for salmon and
trout parr in the River Tornionjoki drainage). Helsinki RKTL. 11 p. (Mimeogr.)
Toivonen, J. 1962. Kalastus. Tornionjoki C 1:3. (Fishery in the River Tornionjoki).
Imatran Voima Gy. 22 p.
9
Table 1. Information' from three example rivers in the Gulf of 80thnia - cases of Rbier
Simojoki, Tornionjoki and Vindelälven (Toivonen 1962, Karlsträrn 1977; Jutila 1987,
Jutila 1992, Jutila & Pruuki 1988, Romakkaniemi 1988, FGFRI, unpublished). The
values are only rough estimates based on several data sets, caleul~tion proeedures,
stocking experiments ete.
.,
SIMOJOKI TORNIONJOKI. "VINDELÄLVEN . .
INFORMATION FROM RIVER
SYSTEMS:
520
370
170
River length, main stern, km
800 - 900
290
110
River, aeeessible for salmon, km
Mean disehan:~e, m;;/s
38
380
180
40010
11 910
River catehment area, km 2
3130
0.095
Mean gradient, %
0.103
0.091
1
830
approx. 15 000 )
5700
Total f1uvial habitat aeeessible for
salmon, ha
Total estimated nursery area for
255
5000
1 000
salmon, ha
Estimation range of nursery area,
234-293
2342 - 5 250
main stern, ha
130-180 1 ) ............ 3.112 ............ .. "
Grade A nursery. area, ha
...
730 ..
REFERENCE POINTS:
Potential smolt production,
75000
500000
200000
ind.JYear
Potential mean parr density,
15-20
5-15
10-15
ind.J100 m 2 nurse..y habitat
40 2 )
Highest recorded river catch
5-10
300·400
level;tons/year . ' ., ,,,
.... ....
.... , .
....... ...........
.".
'"
INFORMATION FROM STOCK
CHARACTERISTICS:
Sex ratio, % females
29
39.8
Mean weight female/male, kg
5.4/2.3
5.2/2.4
1 200;;)
Mean feeundity, eggs/kg
1 316
1477
Sea. age composition female/male,
9,50,41 4 ) /
9,45,42,4/
% 1SW, % 2SW, % 3SW...
67,25,8 4 )
72,22,5,1
1) Value not established
2) No cateh statistics available from the era of "full produetion"
3) Some old data sets indicate a lower feeundity than shown in the Table 2.
4) 3SW and 4SW eombined
>c·
'l,,"
.
"..;,;''"
".,.-,,\;.'.'......
•
10
Table 2. Mean weight, meari fecuridity (total eggs) and relative fecundity (eggs/kg)
of salmon females from different rivers in the Gulf of Bothnia. Most females were of
wild origin.
..
..
.-., ,-. ,-,' .,.".,...... ,., ...........,." ,-.
. "." . "
Source
River
No of
Mean
Relative
Year
Mean'
femare weight, kg fecundity, fecuridity,
.... ... ,
No eggs, eggs/kg
.........
, ..
.,,"-': ..•. ....., 1-""" ",
"
,- .'
""Sima
7923
1254
1
1986
20
6.3
1166
1
Sima
1987
26
8.9
10374
9976
1426
1
Sima
1988
14
7.0
5995
1145
1
Sima
1989
17
5.2
11608
1389
Sima
1990
59
8.4
1
Simo
1991
30
7.0
9294
1320
1
11006
1992
23
7.3
1511
1
Sima
1316
9454
Sirno
Mean
27
7.2
7.0
9444
1350
1
Tarne
1992
121
' 9.1
6419
704
1*
Torne
1993
44
9444
1350
Mean
7.0
Tarne
121
1201
2
Lögde
1991
6
7.3
8768
.. 5.7
2
Lögde
1993
6506
1141
8
6.5
7637
1171
Lögde
Mean
7
1991
5.7
6654
1167
2
26
Bvske
2*
1992
5.6
4375
781
16
Bvske
Mean'
26
5.7
6654
1167
Byske
302
5.5
8246
1525
3
1977-81
Ume
1993
5.0
7170
1428
4
13
Ume
5.3
7708
1477
Mean
158
Urne
1992
3
10.0
11565
1157
2
Öre
5.9
1119
2
1993
11
6603
Öre
7.95
9084
1138
Öre
Mean
7
".".'.
'~""''',··'d_'·'
"
'.'.-
-~
','
.
'0'
'
0'-""''..
...•
-.' ..
;
...
~"
* S'ti-ippirig obviausly incomplets, values not used for averages
Sourees:
1. Juhi:mi Rytilahti, Finnish Game & Fisheries Res. Institute, Lauiiosaari
and Simojoki hatcheries. . .
.'
,
.
2. Ulf Carlsson, Project Västerbottenslax, Länsstyrelsen i Västerbottens
län, Sweden
3. Bräririäs et al. 1985. ,
.
,4. Harald Johansson, hathchery manager in Norrfors, Sweden.
...4
11
•
:... ' .
Table 3. Mean weight and SO by sex and age of wild and reared salmon eaught in
the trap in Norrfors, River Ume, in 1994. The values are caleulated from 737
salmon, of whieh 620 were of wild origin and 410 were females.
. ,,:.
".,
'"
....
.
. . o.1SW ... '" .
"., Female" I, Male "-0"
.
0"
I Reared
I Wild
Mean,
. kQ
.,
. .,
~
.
.<;
"
",,'
'o_'o·o .. ·.. 2SW,.. "",' .'.
_Female ..
Male .....
so,
Mean,
kQ
so,
kQ "'
0.50
0.14
1.84
1.62
0.50
0.59
5.57
5.44
1.43
1.43
Mean, so, Mean,
.. kQ
···ka .- I,ka
kQ
1.87
1.49
5.20
4.21
"M
co,'.. , . . ,
3SWo- '.' ." .
..Feniale, . ~ .', Male ....
"0,.'
"
Mean,
kQ
--.
.., ,. " . , . . . . . • ., .·M' ..••
0'.
kQ
so,.
I',·
2.47
2.33
..
"-'"
••-
so,
kQ .
I·····
Mean, so,
'.-. kä;· ... kg~~,
7.33
8.51
1.52
2.06
7.69
8.69
0.66
1.18
Table 4. Summaryof age and sex distribution in eoastal and river fishery in the Gulf
of Bothnia. The values of the eoastal, river and broodstoek fishery äre based on
Swedish tag reeoveries from the years 1966-1994 originating from the salmon ofthe
Rivers Lule, Angermanälven and Indalsälven. The trap eateh in Norrfors, RiverUme,
has been eolleeted duHng the years 1985-1994. The mean nurnber of sarnples/year
has been 202 in the eoastal fishery, 90 in the river fishery,' 23 in the broodstoek
fishery and 1141 in the trap cateh in Norrfors.
".
~'",
'-.','
'.
.~. ','.'.
Coastal ",' ""-" ".-- , ,,--,
River
Sroodstoek fishery., ",.
Trap in Norrfors, R. Ume
'
'c,',
_•• ' . , ' . ' ' . , ' "
...•
. ,,,,,.--'"
1SW, '"
.......
,
"-."-,,,.
.
.
...>.1- ",.'
'.
31
48.4
56.3
43.8
19.4
11.4
3.2
10.2
50.7
38.6
34.4
35
"...,'
3SW."~-,,
2SW", .. "
% ofall
%
% ofall
%
female .,. aaes " .female
aaes
..• ~,- ",
~-
n
-- .- ,,,.
..'
".,
,.--
_ , ,.--'...... 4SW." ," ,"
%
%
% ofall
% of all
." aaes" female .~ acies. female
41.9
37.9
37.3
55
15.7
13
9.3
21.2
72.1
78.3
83.8
78.9
2.6
60.7
Table 5. Three example rivers with Saltie salmon: total egg deposition requirements
and eonsequent spawning stocks in numbers offish (females) calculated using the
lowest and the highest values in the range (70-700 eggs/100 m2 ) calculated in
ehapter 4, the Canadian egg deposition target and salmor'i stock enaraeteristics in
the Table 1. The mean weight of female salmon in the Rivei" Simojoki is missing and
the corresponding Tornionjoki value has been used for Simojoki calculations.
,
-
-.-.
Simojoki . , ..
Eggs,
No of
million females
EGG DEPOSITION VALUES:
"Saltie estimate", for the total
nursery area of salmon:
Lowest value: 70 eQQs/100 m2
Highest value: 700 eggs/100 m2
Canadian target, for the total
fluvial habitat:
240 eggs/100 m2
,
.",.,.,
..
.•
,"",,' . " ' "
'~,"
.. -.
""" ••_
,'N
"' Tornionjoki ,,. .'o.Vindelälven.,..
Eggs,
No of
No of
Eggs,
million fernales million females
1.8
18
250
2500
35
350
5400
54000
7
70
910
9100
20
2800
360
55600
137
17800